Known inboard boat drives have a steering and propulsion unit arranged underwater, which can pivot about a vertical axis. The boat is propelled by one or two propellers, whose rotational axis can be pivoted by means of a steering unit. By virtue of the pivotability of the rotational axis of the propellers, a steering effect of the boat is produced. The propulsion and steering unit has a column arranged vertically, which accommodates the driveshaft for the propeller and which passes through an opening in the hull of the boat. In the area of the opening there is an annular gap around the column, the dimensions of which differ and are variable depending on manufacturing and assembly tolerances and on the operating conditions. The annular gap has to be sealed so that no water can make its way into the inside of the boat's hull.
In known boat drives the pivotable steering and propulsion unit is supported and sealed relative to the opening in the hull, for example by elastic rings. The reaction forces that result from the propeller thrust are then transmitted to the hull of the boat by the elastic rings. Examples of this are described in the documents WO 2012/038305 A1 and DE 2748276 A1. In the arrangement according to DE 2748276 A1 the boat drive is fastened to the hull of the boat by flexible fastening elements. The flexible fastening of the boat drive in the boat's hull has the consequence that at the opening between the vertical column of the boat drive and the rim of the opening in the boat's hull, a variable annular gap is produced, which has to be reliably sealed by a sealing arrangement.
With the known sealing arrangements it is problematic that the elastic rings have to absorb and transmit relatively large forces and at the same time they have to reliably seal an annular gap whose dimensions vary. Accordingly, for such sealing arrangements the choice of material for the sealing rings, particularly in relation to their elasticity, is always a compromise between the two functions of force transmission and sealing. Furthermore, such seals are subject to considerable wear as the result of relative movements between the boat drive and the hull of the boat or between the seal and the component to be sealed. This is particularly relevant in the case of a boat drive, which is suspended elastically relative to the boat's hull and which therefore undergoes oscillations, especially in the vertical direction.